This invention relates to methods of depositing silicon oxides, such as silicon dioxide, over substrates.
In methods of forming integrated circuits, it is frequently desired to isolate components of the integrated circuits from one another with insulative material. Such insulative material may comprise a number of materials, including for, example, silicon dioxide, silicon nitride, and undoped semiconductive material. Although such materials have acceptable insulative properties in many applications, the materials disadvantageously have high dielectric constants which can lead to capacitive coupling between proximate conductive elements. For instance, silicon dioxide has a dielectric constant of about 4, silicon nitride has a dielectric constant of about 8, and undoped silicon has a dielectric constant of about 12. As circuit density increases with device geometries becoming smaller, the associated RC delay time increases, and hence there is a need to reduce capacitance below that of silicon dioxide material. Further as geometries have become smaller, it is much more difficult to conformally deposit layers into contact and other openings having high aspect ratio.
One known way of achieving desired lower dielectric constant silicon oxides, such as silicon dioxide, is to provide suitable dopant atoms within the material. Fluorine is but one example, to provide a fluorinated silicon oxide of the general formula FxSiOy.
One recently developed technique for achieving suitable deposition into substrates having high aspect ratio topography, has been developed by Electrotech Limited of Bristol, U.K., and is referred to as a Flowfill(trademark) technology. In such process, SiH4 and H2O2 are separately introduced into a CVD chamber, such as a parallel plate reaction chamber. The reaction rate between SiH4 and H2O2 can be moderated by the introduction of nitrogen into the reaction chamber. The wafer is ideally maintained at a suitably low temperature, such as 0xc2x0 C. at an exemplary pressure of 1 Torr to achieve formation of a silanol-type structure of the formula Si(OH)4 which condenses onto the wafer surface. Although the reaction occurs in the gas phase, the deposited Si(OH)4 is in the form of a very viscous liquid which flows to fill very small gaps on the wafer surface. And as deposition thickness increases, surface tension drives the deposited layer flat, thus forming a planarized layer over the substrate.
The liquid Si(OH)4 is typically then converted to a silicon dioxide structure by a two-step process. First, polymerization of the liquid film is promoted by increasing the temperature to about 100xc2x0 C. to result in solidification and formation of a polymer layer. Thereafter, the temperature is raised to approximately 450xc2x0 C. to depolymerize the substance and form SiO2. The depolymerization temperature also provides the advantage of driving undesired water from the resultant SiO2 layer.
Doping of such SiO2 layer has in the past been attempted by providing a dopant gas in combination with the gaseous H2O2 and gaseous SiH4 precursors during the initial formation of the Si(OH)4 liquid. Such deposition techniques have not met with much success and few if any suitable chemistries have been discovered for such to date. Most attempts for dopant incorporation in this manner invariably result in the loss of the desired flow-filling properties of the films.
Accordingly, it would be desirable to develop alternate methods of achieving doped silicon oxides, such as silicon dioxides, formed via a process using silicon oxide precursors, such as for example Si(OH)4.
The invention comprises methods of depositing silicon oxide material onto a substrate. In but one aspect of the invention, a method of depositing a silicon oxide containing layer on a substrate includes initially forming a layer comprising liquid silicon oxide precursor onto a substrate. After forming the layer, the layer is doped and transformed into a solid doped silicon oxide containing layer on the substrate. In a preferred implementation, the doping is by gas phase doping and the liquid precursor comprises Si(OH)4. In the preferred implementation, the transformation occurs by raising the temperature of the deposited liquid precursor to a first elevated temperature and polymerizing the deposited liquid precursor on the substrate. The temperature is continued to be raised to a second elevated temperature higher than the first elevated temperature and a solid doped silicon oxide containing layer is formed on the substrate.